The long term objective of the proposed research is to understand how cortical neurons integrate sensory inputs in space and time and hence contribute to sensory perception. The goal of the present application is to elucidate the substrates and mechanisms of rapid, context&#8209;dependent response modulation ("dynamics") in adult rat primary sornatosensory (SI) cortex. We propose to use whole cell recording of intracellular currents in vivo, simultaneous single unit recording from multiple neurons, and optical imaging of intrinsic signals from an expanse of cortex, to characterize the detailed electrophysiological changes that occur in individual SI neurons and in the SI map during stimulation of single whiskers and multiple whiskers. We propose the following specific aims: (1) Examine the spatial spread and temporal pattern of subthreshold input to SI neurons. The sum of the excitatory and inhibitory inputs to a neuron, its subthreshold receptive field, provides the spatial substrate for dynamic integration. We shall use intracellular recording to describe the extent of subthreshold receptive fields as well as the temporal characteristics of single&#8209;whisker responses that are critical for multi-whisker interactions. (2) Exornine cortical integration during temporal modulation -of single whiskers. We have recently used optical imaging techniques to demonstrate a sharpening of the spread of cortical activity with increasing frequency of whisker stimulation. To explicate the changes underlying this paradigmatic case of dynamic integration, we shall record intraceBu1arly from SI neurons during stimulation of individual center and surround whiskers at increasing frequency. (3) Examine cortical integration during multi&#8209;whisker stimulation, particularly as amplitude, frequency and direction of motion of central and surround inputs is varied. We shall carry out parametric studies of multi&#8209;whisker responses, as well as examine specific hypotheses derived from a model of cortical dynamics postulating how interactions between center and surround whiskers sharpen the representation of salient inputs in cortex. Information from these experiments will be important for understanding the integration of multiple inputs in sensory cortex, and more generally for understanding cortical mechanisrns of object detection and discrimination.